ICS 71.100.70  
 
Reference number  
DRS 148:2020  
© RSB 2020  
  
 RWANDA 
STANDARD  DRS  
148 
 
Second edition  
2020 -mm-dd 
 
Carbolic toilet soap — Specification  
   
DRS 148:2020  
©RSB 2020  - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2020  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reprodu ce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 788303492  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw  DRS 148:2020  
iii                ©RSB2020 - All rights reserved  
 Contents  Page 
1 Scope  ................................ ................................ ................................ ................................ ....... 1 
2 Normative references  ................................ ................................ ................................ ..............  1 
3 Terms and definitions  ................................ ................................ ................................ .............  1 
4 Requirem ents ................................ ................................ ................................ ..........................  2 
4.1 General requirements  ................................ ................................ ................................ .............  2 
4.2 Specific requirements  ................................ ................................ ................................ .............  3 
4.3 Basis of Test requirements  ................................ ................................ ................................ ..... 3 
5 Packaging and labelling  ................................ ................................ ................................ ..........  4 
5.1 Packaging  ................................ ................................ ................................ ................................  4 
5.2 Labelling  ................................ ................................ ................................ ................................ .. 4 
6 Sampling  ................................ ................................ ................................ ................................ .. 4 
Annex  A (normative)  Identification of rosin content of fatty matter in soaps  ................................ .. 5 
A.1 Scope  ................................ ................................ ................................ ................................ ....... 5 
A.2 Reagents  ................................ ................................ ................................ ................................ .. 5 
A.3 Procedure  ................................ ................................ ................................ ................................  5 
Annex  B (normative)  Determination of rosin content of fatty matter in soaps  ................................  7 
B.1 Scope  ................................ ................................ ................................ ................................ ....... 7 
B.2 Reagents  ................................ ................................ ................................ ................................ .. 7 
Annex  C (normative)  T exture and stability test  ................................ ................................ ...............  11 
Annex  D (normative)  Determination of carbolic acid content  ................................ .........................  12 
D.1 Scope  ................................ ................................ ................................ ................................ ..... 12 
D.2 Reagents  ................................ ................................ ................................ ................................  12 
Annex  E (normative)  Determination of matter insoluble in water  ................................ ...................  14 
E.1 Scope  ................................ ................................ ................................ ................................ ..... 14 
E.2 Apparatus  ................................ ................................ ................................ ..............................  14 
E.3 Procedure  ................................ ................................ ................................ ..............................  14 
E.4 Calculation  ................................ ................................ ................................ .............................  14 
 DRS 148:2020  
©RSB 2020  - All rights reserved                  iv 
 Foreword  
Rwanda Standard s are prepared  by Technical Committees and approved by Rwanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards adop ted 
by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and gazettment as 
Rwanda Standards.  
DRS 148 was prepared by Technical Committee RSB/TC 042, Surface Active Agents . 
In the preparation of this standard, reference was made to the following standard:  
CD-ARS 1459:2019 , Carbolic toilet soap  — Specification  
The assistance de rived from the above source is hereby acknowledged with thanks.  
This edition  cancels and replaces the second edition (RS  148:2014 ), which has been t echnically revised.  
Committee membership  
The following organizations were represented on the Technical Committee on Surface Active Agents (RSB/TC 
042) in the preparation of this standard.  
University of Rwanda/College of Science and Technology (UR/CST)  
ALYVO Rwanda Ltd  
HORIZON/SOPYRWA  
University of Kibungo (UNIK)  
Standards for Sustainability (SfS)  
Catchup Industries Ltd  
SULFO Rwanda Industries Ltd  
MACPELA Investment Ltd  
Rwanda  Standards Board  (RSB) – Secretariat  DRS 148:2020  
v                ©RSB2020 - All rights reserved  
 Introduction  
A paragraph.  DRS 148: 2020  
1                ©RSB2020 - All rights reserved  
 Carbolic toilet soap — Specification  
1 Scope  
This Draft  Rwanda Standard  specifies the requirements , sampling and test methods for hard toilet soap 
containing additions of phenolic substances such as cresylic acid.  
2 Normative references  
The following documents are referred to in the text in such a way that some or all of  their content constitutes 
requirements of this document.  For dated references, only the edition  cited applies. For undated references, the 
latest edition of the referenced document (including any amendments) applies.  
RS EAS 377 (all parts),  Cosmetics and Cosmetic Products   
RS ISO 457, Soaps — Determination of chloride content — Titrimetric method  
RS ISO 673, Soaps —Determination of content of ethanol -insoluble matter  
RS ISO 684, Analysis of soaps —Determination of total free alkali  
RS ISO 456 , Surface Acti ve Agents — Determination of free caustic alkali  
ISO 4314 , Surface active agents — Determination of free alkalinity or free acidity — Titrimetric method  
RS ISO 1067, Analysis of soaps — Determination of unsaponfiable, unsaponified and unsaponified saponifiable 
matter  
3 Terms and definitions  
For the purposes of this standard, the terms and definitions given in RS ISO 862 and the following apply . 
3.1 
carbolic soap  
a mildly antiseptic soap containing carbolic acid and /or cresylic acid, both of which are  phenols deriv ed from 
either coal tar or petroleum sources  
3.2 
batch  
soap manufactured from one boil or, in the case of continuous production processes, the material from a single 
day’s production   
©RSB 2020  - All rights reserved                  2 
 3.3 
boil 
soap  from pan or vat  
3.4 
defective  
soap  or its container that fails in one or more respects to comply with the appropriate requirements of the 
specification  
3.5 
lot 
that quantity of soap powder or chips bearing the same batch identification and from one manufacturer, 
submitted at any one time for inspe ction and testing  
3.5 
unit 
bar or tablet of soap with no covering  
4 Requirements  
4.1 General  requirements  
4.1.1  The carbolic toilet soap shall be in form of bar or tablet  
4.1.2  The carbolic toilet soap shall be kneaded, uniformly mixed and compressed in firm and  uniform texture  
4.1.3 The carbolic toilet soap may be perfumed. The odour of the soap and the odour when dissolved in 
water shall not be objectionable.  
4.1.4  The carbolic toilet soap shall have a good lathering and cleaning properties and shall not irrit ate the 
skin. 
4.1.5  All the substances used in carbolic toilet soap shall comply with the requirements of all parts of RS 
EAS 377  (all parts) .   
4.1.5 When tested as described in Annex C, the carbolic toilet soap shall not crumble and its surfaces shall 
remain smooth  
4.1.6 The carbolic toilet soap shall remain stable, without any change on its quality performance,  when 
stored under normal storage conditions for a period of six months.  DRS 148: 2020  
3                ©RSB2020 - All rights reserved  
 4.2 Specific  requirements  
The carbolic toilet soap shall comply with the requirements given in Table 1, whe n tested in accordance with 
the methods described therein.  
Table 1 — Specific  requirements of carbolic toilet soap  
S/N  Characteristics  Requirement  
 Test method  
i. Total fatty matter, min.  60.0 ISO 685  
ii. Rosin acids, %  of total fatty matter max.  15.0 Annexes A&B  
 
iv.  
Matter insoluble in ethanol, max.  2.0 
 RS ISO 673  
v. Carbolic acid content, % by mass, min. 1.0 – 3.0  Annex D 
vi. Free caustic alkali as NaOH , % by mass , 
max.  0.1  RS ISO 684 , RS ISO 456  
vii. Total free alkali as NaOH, % by mass, 
max.  0,2  RS ISO 684  
RS ISO 4314  
viii. Free acidity content (as oleic acid), % by 
mass, max.  0.5 
ix. Unsaponofied plus unsaponifiable 
matter content, % by mass, max.  1.0 RS ISO 1067  
x. 
 Chlorides as NaCl, max.  
 0.8 0.5 RS ISO 457  
xi Matter insoluble in water,  % by mass  
max.  0.5 Annex E  
 
4.3 Basis of Test requirements  
4.3.1  The soap covered by this  standard is liable to lose moisture on keeping. The actual results obtained by 
the stated methods of analysis shall therefore be recalculated in relation to the specified minimum total fatty 
matter by means of the equation:  
Recalculated Results = Actual Result x Min. TFM  specified
Actual  TFM  found 
4.3.2  In each case, the requirements indicated in Table 1 shall be satisfi ed if the recalculated result obtained s 
above is within the specified range.  
 
 
  
©RSB 2020  - All rights reserved                  4 
 5 Packaging and labelling  
5.1 Packaging  
Each cake or number of cakes shall be packed in a suitable protective container. A number of cakes shall then 
be packed in suitable boxes or outer packaging to form a tight package,  
5.2 Labelling  
On the package and on each box or carton shall be labelled the following particulars:  
a) the name of the product ‘carbolic toilet soap’ and any other qualifying words where applicable;  
b) the name and address of  the manufacturer or trade mark;  
c) nominal mass of each cake at the time of packing;  
d) on the box or the outer package, the number of cakes contained therein and the date of manufacture; and  
e) commercial brand names may be added as well as details of composition  provided that this further 
information shall not be misleading  
f) information shall not be misleading  
6 Sampling  
Sampling shall be done in accordance with ISO 15528 . Commented [F1]: to appear in normative reference  DRS 148: 2020  
5                ©RSB2020 - All rights reserved  
 Annex  A 
(normative)  
 
Identification of rosin content of fatty matter in soaps  
A.1 Scope  
This annex specifies the Helphen -Grimaldi and Liebermann -Storch method  for the identification of rosin in fatty 
matter.  
A.2 Reagents  
NOTE  Use only analytical reagents and distilled water  
A.2.1 Acetic anhydride  
A.2.2 Sulphuric acid, density 1.53 g/mL. Cautiousl y add 97 mL of sulphuric acid (density 1.84 g/mL) TO 
100 mL of water.  
A.2.3 Solution A. Dissolve 10 g of phenol in 27 mL of chloroform  
A.2.4 Solution B. Dissolve 10 mL of bromine in 40 mL  of chloroform  
A.3 Procedure  
A.3.1 Halphen -Grimaldi method  
A.3.1.1 Place one or two drops of the fatty matter, reserved from the determination of fatty matter (ISO 865), 
in a porcelain basin and add approximately 2 mL of the solution A to dissolve it. Wet the walls of the basin by 
tilting and turning it and let it stand f or a few seconds so that the walls of the basin are covered with a very thin 
film of the solution.  
A.3.1.2 Hold the neck of the flask containing the solution B in such a position that the bromine vapour diffuses 
into the porcelain dish and comes into conta ct with the walls. In the presence of rosin a blueish -grey to purple 
colour develops immediately.  
A.3.1.3 Carry out a comparison test with a sample of fatty matter to which 2 % ( m/m) of rosin has been added.  
NOTE  Should the colour reaction in A.3.1.2 be masked by other colours, conduct a second qualitative test, using the Liebermann -
Storch method.  
A.3.2 Liebermann -Storch method   
©RSB 2020  - All rights reserved                  6 
 A.3.2.1 Place 1 g - 2 g of the fatty matter in a test tube, add 5 mL - 10 mL of the acetic anhydride, and heat 
the mixture in a b oiling water bath for approximately 3 min. Cool to room temperature and pour 1 mL - 2 mL of 
the solution into a white porcelain basin.  
A.3.2.2 Allow one or two drops of the sulphuric acid to run down the side of the basin. If rosin is present, a 
violet col our immediately develops where the acid is in contact with the solution. This colour then turns brown 
on standing.  
A.3.2.3 Carry out a comparison test with a sample of fatty matter to which 2 % ( m/m) of rosin has been added.  DRS 148: 2020  
7                ©RSB2020 - All rights reserved  
 Annex  B 
(normative)  
 
Determination of rosin content of fatty matter in soaps  
B.1 Scope  
This annex specifies a method for the determination of the rosin content of fatty matter in soaps  
NOTE 1  Before proceeding with the quantitative of rosin, first establish its presence by a qualitative test (see Annex A).  
NOTE 2  The following method is not accurate for rosin concentrate below a mass fraction of 5%.  
B.2 Reagents  
NOTE  Use only analytical reagents and distilled water  
B.2.1  Diethyl ether  
Free from peroxides  
B.2.2  Sodium chloride  
B.2.3  Sodium sulfate, anhydrous  
B.2.4  Hydrochloric acid solution  
Dilute one volume of concentrated hydrochloric acid (density 1.16 g/mL) with two volumes of distilled water.  
B.2.5  Sodium hydroxide solution  
10% mass fraction aqu eous solution  
B.2.6  Naphthalene -2-sulfonic acid soluti on 
Dissolve 40 g of naphthalene -2-sulfonic acid in 1 L of absolute methanol  
B.2.7  Sodium chloride solution, saturated  
Shake an excess of sodium chloride with water at ambient temperature until no more dissolves. Keep the 
solution over solid sodium chloride . 
B.2.8  Sodium chloride solution, 10 %   
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Dissolve 10 g of sodium chloride in 100 mL of water.  
B.2.9  Standard ethanolic potassium hydroxide solution, 0.2 N  
B.2.9.1  Preparation  
Purify 95 % (by volume fraction) ethanol by boiling 1.5 L of it over 20 g of potassium hydroxide for 1 h under 
reflux. Distil, discarding the first 50 mL of the distillate and stopping the distillation when approximately 1.3 L 
have been distilled. Dissolve 12 g of potassium hydroxide in 1 L of the purified ethanol, allow the soluti on to 
stand for approximately one week, and then decant the clear supernatant liquid from any potassium carbonate 
that has precipitated.  
B.2.9.2  Standardization  
Accurately weigh out approximately 1 g of potassium hydrogen phthalate (previously dried at 110  °C ± 5 °C for 
3 h) into a 250 mL Erlenmeyer flask. Add approximately 100 mL of carbon dioxide -free distilled water and three 
drops to five drops of the phenolphthalein indicator, and swirl gently until the solid has dissolved. Titrate the 
solution with th e standard ethanolic potassium hydroxide solution, until a permanent pink colour is formed.  
B.2.9.3  Calculation  
Normality of the standard ethanolic potassium hydroxide solution ( N): 
B.AN8974
 
where  
A is the mass of the potassium hydrogen phthalate, in grams;  
B is the volume of the standard ethanolic potassium hydroxide solution used for the titration, in 
millilitres.  
B.2.10  Methyl orange indicator  
Dissolve 0.2 g of methyl orange in 100 mL of carbon dioxide -free water.  
B.2.11  Phenolphthalei n indicator  
Dissolve 0.5 g of phenolphthalein in 100 mL of freshly boiled, 95 % (by volume fraction) ethanol.  
B.3 Procedure  
B.3.1  Preparation of fatty matter  DRS 148: 2020  
9                ©RSB2020 - All rights reserved  
 B.3.1.1  Carbolic soaps  
B.3.1.1.1 Weigh out accurately into a 600 mL beaker such quantity of the te st sample as contains approximately 
40 g of fatty matter and dissolve it in approximately 400 mL of hot water, to which 40 mL of the sodium hydroxide 
solution has been added.  
B.3.1.1.2 Salt out the soap by adding sufficient sodium chloride to the hot solut ion to saturate it (at ambient 
temperature) with sodium chloride. Filter the soap quantitatively, and allow it to drain.  
B.3.1.1.3 Dissolve the drained soap in approximately 400 mL of hot water, and repeat the salting out and filtering 
procedure.  
B.3.1.1.4 Wash the soap thoroughly with the saturated sodium chloride solution, and proceed in accordance 
with B.3.1.2.2 to B.3.1.2.7.  
B.3.1.1.5 Reserve the combined filtrates and washings for the determination of carbolic acids.  
B.3.1.2  Other soaps  
B.3.1. 2.1 Weigh accurately into a 600 mL beaker such quantity of the test sample as contains approximately 
40 g of fatty matter.  
B.3.1.2.2 Dissolve the soap in approximately 400 mL of hot distilled water, cool the solution, and slowly add an 
excess of the hydroc hloric acid solution. Cover the beaker with a watch -glass and heat the contents until the 
fatty matter separates into a clear layer, but do not allow the temperature to exceed 60 °C.  
B.3.1.2.3 In the cases of liquid and gel soaps, acidify the soap as it is . 
B.3.1.2.4 Cool to approximately 25 °C and transfer the contents of the beaker to a separating funnel. Rinse the 
watch -glass and the beaker with portions of the diethyl ether totalling 100 mL and add them to the separating 
funnel. Shake the mixture in the  separating funnel vigorously for 1 min, and let it stand until the two phases have 
separated.  
B.3.1.2.5 Draw off and discard the aqueous layer and wash the ether extract with 50 mL portions of the sodium 
chloride solution until the last washing is neutral  to the methyl orange indicator.  
B.3.1.2.6 Filter the washed ether extract into a 250 mL beaker through a filter paper containing approximately 
5 g of anhydrous sodium sulfate, and wash the separating funnel and the filter with small portions of the diethy l 
ether.  
B.3.1.2.7 Evaporate the ether extract plus washings on a warm water bath. When the residue is just dry, heat 
it rapidly to 130 °C and immediately place the beaker in a desiccator to cool.  
NOTE  B.3.1.2.2 to B.3.1.2.7 should be completed in the shor test possible period of time, so as to prevent oxidation of the fatty acids.  
B.3.2  Determination of rosin content   
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 B.3.2.1  Weigh accurately into a 150 mL flask with a ground -glass joint approximately 2 g of the prepared fatty 
matter (B.3.1.2.7) and reserve the rest in the case of soap powders for the fatty matter titre determination.  
B.3.2.2  Add exactly 25 mL of the naphthalene -2-sulfonic acid solution to the flask and two or three glass beads, 
and boil under reflux for 30 min.  
B.3.2.3  Carry out a blank test  at the same time, using exactly 25 mL of the naphthalene -2-sulfonic acid solution 
only.  
B.3.2.4  Cool the contents of both flasks (sample and blank) to ambient temperature, add 0.5 mL of the 
phenolphthalein indicator to each flask, and immediately titrate to the end point with the standard ethanolic 
potassium hydroxide solution.  
B.4 Calculation  
Rosin content of fatty matter, as a mass fraction percentage ( R): 
0.16.34 ) (CNBAR
 
where  
A is the volume of the standard ethanolic potassium hydroxide solution  used for the titration of 
the sample solution, in millilitres;  
B is the volume of the standard ethanolic potassium hydroxide solution used for the titration of 
the blank solution, in millilitres;  
N is the normality of the standard ethanolic  potassium hydroxide solution;  
C is the mass of the fatty matter taken, in grams.  
Dissolve 10 g of sodium chloride in 100 mL of water  
  
 
 DRS 148: 2020  
11                ©RSB2020 - All rights reserved  
 Annex  C 
(normative)  
 
Texture and stability test  
A whole cake of soap is immersed in distilled water at a temperature of 25 ºC — 30 ºC contained in a vessel of 
one litre capacity. After one hour the cake is removed from water, allowed to dry at room temperature for 
24h and then examined for crumbling and smoothness on its surfaces . It shall not crumble crack or break.  
 
 
   
©RSB 2020  - All rights reserved                  12 
 Annex  D 
(normat ive) 
 
Determination of carbolic acid content  
D.1 Scope  
This standard specifies a method for the determination of the carbolic acid content of carbolic soap.  
D.2 Reagents  
NOTE  Use only analytical grade reagents and distilled water  
D.2.1  Diethyl ether , free from per oxide  
D.2.2  Sodium sulfate , anhydrous  
D.2.3  Hydrochloric acid solution  
Dilute one volume of concentrated hydrochloric acid (density 1.16 g/mL) with two volumes of water.  
D.2.4  Methyl orange indicator  
Dissolve 0.2 g of methyl orange in 100 mL of water.  
D.3 Procedure  
D.3.1  Transfer the combined filtrates and washing retained from the determination of rosin content (see 
Annex B) quantitatively to a separating funnel, add a few drops of the methyl orange indicator, and then slowly 
add the hydrochloric acid solution until there  is an excess of about 5 mL.  
D.3.2  Extract the acidified solution with 100 mL and then three times with 30 mL portions of the diethyl ether. 
Combine the ether extracts in a second separating funnel and wash four times with 20 mL portions of water.  
D.3.3  Combine the washings and extract them with approximately 30 mL of the diethyl ether. Wash this 
extract with water until the washings are neutral to the methyl orange indicator and add this washed extract to 
the ether extract in the second separating funnel.  
D.3.4  Filter the combined extracts into a 500 mL beaker through a filter paper containing approximately 5 g 
of the sodium sulfate. Wash the separating funnel and the filter thoroughly with small portions of the diethyl 
ether.  
D.3.5  Evaporate off approximat ely two -thirds of the ether on a hot water bath, transfer the concentrated 
ethereal solution quantitatively to a tared crystallizing dish, using small portions of the diethyl ether to rinse the 
beaker, and evaporate to dryness on a hot water bath.  DRS 148: 2020  
13                ©RSB2020 - All rights reserved  
 D.3.6  When just dry, leave the dish for a further 3 min on the water bath, and remove the last traces of ether 
by means of a current of dry air. Let the dish and its contents cool in a desiccator and weigh.  
D.4 Calculation  
Carbolic acid content, as a mass fraction  percentage ( M): 
NBMAM100
 
where  
A is the mass of the residue, in grams;  
B is the mass of the test sample used, in grams (see Annex B);  
M is the required minimum fatty matter content of the sample, as a percentage;  
N is the actual fatty matter  content of the sample, as a percentage.  
 
  
©RSB 2020  - All rights reserved                  14 
 Annex  E 
(normative)  
 
Determination of matter insoluble in water  
E.1 Scope  
This annex  specifies a method for the determination of the water insoluble matter content of soap products.  
E.2 Apparatus  
E.2.1  Oven. A drying oven capable of being maintained at 105 ± 5 ºC 
E.3 Procedure  
E.3.1   Soap powders, gel soaps  
Thoroughly wash the residue on the glass fibre filter, retained from the determination of free alkali content and 
free acid content, with hot distilled water. Dry the residue and the filter in the oven maintained at 105 ± 5 °C, 
cool in a desiccator, and weigh.  
E.3.2  Scouring compounds  
Dry the residue and the filter, retained from the determination of alkaline salts, in the oven maintained at 105 ± 
5 °C, cool in a desiccator, and weigh. Repeat the drying and weighing procedure until no further loss in mass 
occurs.  
E.4 Calculation  
C.4.1  Soap powders, gel soaps  
Water insoluble matter content, 
NBMA
100%(m/m)  
where  
A = mass of the residue, g  
B = mass of the test s ample used, g  
M = required minimum fatty matter content of the sample, %  
N = actual fatty matter content of the sample, %.  DRS 148: 2020  
15                ©RSB2020 - All rights reserved  
  
C.4.2  Scouring compounds  
Water insoluble matter content, 
BA100 %(m/m)  
where  
A = mass of the residue, g  
B = mass of the test sample used, g.  
 CD 148: 2020  
 
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